Muller - Lyer Illusion

1. Muller - Lyer Illusion

2. Muller - Lyer Illusion

3. Muller-Lyer Illusion What theory does Gregory take up?

4. Muller-Lyer Illusion What theory does Gregory take up? Thiery / Woodworth : Muller-Lyer figure “suggests perspective”

5. Muller-Lyer Illusion What theory does Gregory take up? Thiery / Woodworth : Muller-Lyer figure “suggests perspective” Is there something about the presence of pictorial depth cues in an image that distorts size?

6. Depth Cues and Size Distortion The Ponzo Illusion:

7. Depth Cues and Size Distortion The Ponzo Illusion:

8. Depth Cues and Size Distortion The illusion of depth in an image seems to distort the perception of size in the image This is due to misapplication of Size - Constancy

9. Pictures are Weird What does Gregory find paradoxical about pictures?

10. Pictures are Weird What does Gregory find paradoxical about pictures? Pictures convey depth yet also appear flat Why?

11. Pictures are Weird When you view a picture there are some depth cues telling you to perceive depth, but other cues telling you that the image is on a flat surface …the surface matters!

12. Pictures are Weird • Retinal image size

13. Pictures are Weird • Retinal image size

14. The Apparatus What does Gregory do to remove the paradox so that the Muller-Lyer figure no longer looks flat? Remove the background surface

15. The Apparatus

16. Removing the Background With background removed, Muller-Lyer figure actually looks3D

17. Removing the Background What prediction can you make about how the perceived size and the perceived distance of the center line are related?

18. Removing the Background What prediction can you make about how the perceived size and the perceived distance of the center line are related? When the centre line appears close, it should also appear small When the centre line appears far, it should also appear large

19. Removing the Background How did Gregory test that?

20. The Apparatus

21. Removing the Background Perceived size and perceived distance are tightly related inward arrowheads make line look closer / outward arrowheads make line look farther

22. Seeing in Stereo Seeing in Stereo

23. Seeing in Stereo It’s very hard to read words if there are multiple images on your retina It’s very hard to read words if there are multiple images on your retina

24. Seeing in Stereo It’s very hard to read words if there are multiple images on your retina It’s very hard to read words if there are multiple images on your retina But how many images are there on your retinae?

25. Binocular Disparity • Your eyes have a different image on each retina • hold pen at arms length and fixate the spot • how many pens do you see? • which pen matches which eye?

26. Binocular Disparity • Your eyes have a different image on each retina • now fixate the pen • how many spots do you see? • which spot matches which eye?

27. Binocular Disparity • Binocular disparity is the difference between the two images

28. Binocular Disparity • Binocular disparity is the difference between the two images • Disparity depends on where the object is relative to the fixation point: • objects closer than fixation project images that “cross” • objects farther than fixation project images that do not “cross”